1. Field of the Invention
The present invention relates to an optical disc device capable of performing data recording or reading by irradiating an optical disc with light, and more specifically, to an optical head that irradiates the optical disc with light.
2. Description of the Prior Art
In recent years, as a recording medium for data such as pictures and sounds, optical discs have been widely used which are capable of performing data recording or reading by being irradiated with light. As the optical disc, a CD (compact disc), a DVD (digital versatile disc), and the like are widely used. An optical disc device, which performs data recording or reading on this optical disc as a recording medium, includes an optical head that irradiates the recording surface of the optical disc with laser light and that detects the light reflected therefrom.
FIG. 6 is a schematic layout drawing of a DVD player as one example of a conventional optical disc device. The DVD player PM shown in FIG. 6 includes: a spindle motor Sp that rotates a DVD media Ds; an optical head B that irradiates the surface of the DVD media Ds with laser light and then detects the light reflected therefrom; a decoder Dc that decodes a signal detected by the optical head B; an external connector Oc that makes connection with an external monitor Mn; and a controller Cont.
First, the controller Cont drives the spindle motor Sp to thereby rotate the DVD media Ds. The optical head B irradiates the DVD media Ds in rotation with laser light, and then detects the light reflected therefrom. The light detected by the optical head B is transmitted as an electrical signal to the decoder Dc, where the signal is demodulated into a picture signal and then is transmitted to the monitor Mn, whereby the picture is displayed on the monitor Mn.
FIG. 2 shows a layout drawing of the optical head. The optical head has, as shown in FIG. 2, a laser light source Ld, a mirror Mr, a collimating lens 3, an objective lens 4, a beam splitter Bs, and a light receiving element Pd. Laser light emitted from the laser light source Ld is reflected on the mirror Mr and then enters the collimating lens 3. The laser light entering the collimating lens 3 then emerges therefrom as parallel light and then enters the objective lens 4. The laser light entering the objective lens 4 is irradiated to the recording surface of the DVD media Ds.
At this point, the laser light is irradiated, focusing on a recording layer of the DVD media Ds, so that the optical axis and the recording layer of the DVD media Ds become perpendicular to each other. The beam splitter Bs is a prism that transmits half of incident laser light therethrough and reflects half of the incident laser light and that guides light reflected on the DVD media Ds to the light receiving element Pd. The light receiving element Pd converts light into a current, and reads data based on the intensity of light.
FIG. 7 is a perspective view of a conventional optical head, and FIG. 8 is a sectional view thereof. As shown in FIG. 7, the optical head B has a base 91 for fitting the collimating lens 3, and an actuator base 92 (hereinafter indicated as act base) which is fitted to the base 91 and on which the objective lens 4 is arranged. As shown in FIG. 7, the act base 92 is fixed to the base 91 with three sections thereof screwed with, but not limited to, screws 93 in this embodiment. Considering the symmetry property, one of the screws 93 for fixing the act base 92 is fitted with a spring 94. The act base 92 is always biased by the spring 94. The objective lens 4 is so arranged by being fitted to a lens fitting part 95, which is then fitted to the act base 92.
As shown in the sectional view of FIG. 8, in the base 91, a large truncated spherical recession 911 is formed. On the act base 92, the projections 921, not limited to but three in quantity in this embodiment, are formed which are cut into a spherical shape. The curved surface of this projection 921 is arranged in contact with the curved surface of the recession 911. As shown in FIG. 8, by tightening and loosening the screw 93, the curved surface of the projection 921 moves while making contact with the curved surface of the recession 911, whereby the act base 92 smoothly changes its tilt state with respect to the base 91.
The act base 92 is tilted by adequately operating the screws 931 so that the DVD media is irradiated with laser light emitted from the objective lens 4, with the optical axis thereof perpendicular to the DVD media. Subsequently, an adhesive Be is applied to the side surfaces of the base 91 and the act base 92, whereby the act base 92 is fixed to the base 91. In this manner, the optical head B can be manufactured.
The collimating lens 3 fitted to the base 91 and the objective lens 4 included in the act base 92 are generally so formed as to be arranged vertically one on another at position where laser light is shined. However, when the relative position between the collimating lens 3 and the objective lens 4 exceeds the permitted range due to deformation at manufacturing or the like, the screws 93 (930, 931), and the recession 911 and the projections 921 may not be arranged at respective positions within the permitted ranges since they cannot be largely shifted.
Thus, a three-dimensional bonding method as shown in FIG. 9 may be adopted. An optical head C shown in FIG. 9 has a through hole 811 in a base 81. A positioning member 86 penetrating through this through hole 811 is used for positioning. The positioning member 86 is formed in a rectangular parallelepiped shape, having on the top thereof two projections 861 formed in a cylindrical shape with a magnet 862 in between. In the act base 82, locking holes 821 are formed at position in correspondence with the projections 861. The positioning member 86 is penetrated through the through hole 811, then the projections 861 of the positioning member 861 are put into engagement with the locking holes 821 of the act base 82, and then the positioning member 86 and the act base 82 are firmly connected together.
Subsequently, the positioning member 86 is moved horizontally to move the act base 82 so that the objective lens 4 arranged on the act base 82 is located at such a position as to appropriately receive laser light emerging from the collimating lens 3 fitted to the base 81. Further, moving the positioning member 86 makes adjustment so that the DVD media is irradiated with the laser light emerging from the objective lens 4, with the optical axis thereof perpendicular to the DVD media. Subsequently, upon completion of this adjustment, the adhesive Be is applied to the side surfaces of the base 81 and the act base 82, whereby the act base 82 is fixed to the base 81.
The invention as described in JP-A-2002-42373 refers to a method of fixing a stator part of an actuator to a frame by inserting a fixing projection through a fixing through hole with an adhesive.
However, bonding by use of the spherical recession 911 and the projections 921, the screws 93 (930, 931), and the spring 94 cannot support a case where the collimating lens 3 and the objective lens 4 are largely dislocated from the designed arrangement position. In case of adjustment made by the screws 93 (930, 931), small adjustment is difficult and the screws 93 (930, 931) cannot be detached after the adjustment; thus, a larger number of components is required accordingly. Moreover, it is difficult to evenly apply the adhesive Be or the like.
With the method shown in FIG. 9, the position where the act base 82 is to be arranged is determined by use of the positioning member 86, and the act base 82 and the base 81 are bonded together with the adhesive Be. In this operation, when it is difficult to apply the adhesive Be or the like evenly to different spots and thus it is not evenly applied, a biased stress is imposed on the act base 82 under shrinkage of the adhesive Be or the like. Under influence of this biased stress, the act base 82 moves to a position not determined by the positioning member 86 or is so fixed as to be deformed, thereby leading to performance degradation of the optical head.
The invention as described in JP-A-2002-42373 discloses a method of inserting a fixing projection through a fixing through hole and then fixing them with an adhesive. However, this provides a structure such that the adhesive tends to flow out of the gap between the fixing projection and the fixing through hole, so that unequal stress is possibly generated due to adhesive condensation.